The plan is straightforward. If Brazil, China, Europe and the USA can take a lead on this issue then our chances of preventing catastrophic climate change soar. But there's no way those nations will do what's necessary unless their leaders get hands on and actually lead.

So Lula, Hu, the leaders of Europe and President Obama need to take the first step and commit to attending the summit in person. We all know they're not going to let their environment ministers sign them up to the most important treaty in history. They need to do this one themselves.